1. Field of the Invention
The present invention relates generally to cooling of jet engine components having a surface exposed to a hot gas flow and, more particularly, to cooling arrangements providing a plurality of holes for passage of fluids for cooling of such components.
2. Description of the Prior Art
Gas turbine engines conventionally comprise an axial flow compressor which compresses air to the proper pressure required for supporting combustion of fuel in a combustion chamber. The combustion gases then pass to a turbine which powers the axial flow compressor. After passing through the turbine, the high energy combustion gas flow may be employed to drive a power turbine which is connected to an output shaft on which may be mounted a propeller, fan or other device. Alternatively, the high energy combustion gas flow may be utilized directly as a thrust to provide motive power, as in turbojet engines commonly used for aircraft.
It is well known that efficiency of jet engines, such as gas turbine, ramjet and scramjet engines used to power aircraft, ships, tanks, electric power generators, etc., increases with increase in temperature of the combustion gas flow. A limiting factor in the gas flow temperature is the high temperature capability of the various jet engine components, such as turbine, stator and rotor airfoils, exposed to a hot gas flow. Various approaches to internally cooling these engine components have been proposed to increase the upper operating temperature capability of the engines.
One advantageous approach is "film cooling" of the jet engine components exposed to the hot gas flow. The term "film cooling" refers to the technique of cooling the external surface of the engine component, being heated by the hot gas flow, by injecting a relatively cooled fluid, such as air, along the external surface. The cooled fluid moves sufficiently slow so that it acts as an insulative layer to reduce unwanted heating of the external surface of the engine component by the adjacent hot gas flow stream.
It is conventional to provide cooling holes and passages through a wall of the engine component to exhaust pressurized cooling air flow from an interior chamber through the wall of the engine component to the exterior surface which is exposed to the hot gas flows. Examples of different arrangements and configurations of cooling holes and passages that have been proposed in the prior art are disclosed in U.S. patents to Howald (3,527,543), Hauser et al (3,819,295 and 3,934,322), Corrigan (4,221,539), Durgin et al (4,297,077), Vehr (4,653,983) and Auxier et al (4,664,597), and in a European patent application to Marriage (EP 0 375 175 Al).
Although the hole and passage configurations of the cited documents are steps in the right direction for providing cooling of engine components exposed to the hot gas flow in order to increase the operating temperature and thereby the efficiency of the jet engines, a need for additional improvement still remains.